In a typical electrostatographic reproducing apparatus, a light image of an original to be copied is recorded in the form of an electrostatic latent image upon a photosensitive member. The latent image is subsequently rendered visible by the application of electrostatically charged thermoplastic resin particles which are commonly referred to as toner. The developed image is then fixed to the imaging surface or is transferred to a receiving substrate, such as paper, to which it is fixed by a suitable fusing technique involving the application of heat, resulting in a xerographic print or toner-based printed substrate.
The xerographic print presents a complex array of surface energies and wetting responses. The surface energy of toner depends on its composition and in general varies from that of the paper to other substrate, which itself exhibits considerable variation depending on its composition, presence of coating, etc. Additionally in the case of xerographic print engines employing fuser oils, the surface energy of each component is altered by the level and nature of the fuser oils present, as well as the interaction between the oil, toner, and substrate. Finally, there is variable roughness and porosity associated with both toner (e.g., half-tone screens versus solids) and substrate, which affects the wetting response. The variability in surface energy and wetting response is measurable over a range of scales using familiar techniques involving sessile drop contact angles.
There are many situations where it is desirable to modify xerographic print surfaces to be less hydrophobic or have a hydrophobic/hydrophilic balance over a scale range according to their applications. For example, in some biomedical/pharmaceutical situations, water-based test fluid placed on a printed target image is required to wet the printed image surface but not spread thereon. Furthermore, the target prints may involve image and non-image regions, requiring a uniform wetting response across both regions. Thus, there is a need to develop methods and apparatus to control the surface wettability of xerographic prints.